The objective of the proposed research is to study the structure, taxonomy and other features of the protozoa of the phylum Apicomplexa and to prepare an uptodate classification thereof. This phylum comprises about 4,000 species, all parasitic. It includes about 1,400 species of grenarines (parasites of invertebrates), about 1,500 of coccidia (which cause serious disease primarily in domestic and wild animals), several hundred of malaria and related parasites (which cause serious disease in man and other animals), several hundred of haemogregarines (which may cause disease in many wild and domestic animals but are not well understood), and about 100 of piroplasmids (which cause serious disease in domestic and wild animals). The scientific literature on the group will be studied and problems of nomenclature and terminology elucidated. A search will be made for new species of Apicomplexa by microscopic examination of discharges and tissues of various potential hosts. Careful descriptions of those which are found will be published. Cross-transmission studies and testing of appropriate potential transport and intermediate host will be carried out. On the basis of the findings of these studies, an uptodate classification of the Apicomplexa will be developed.